Method And Device For Automatically Monitoring The Ability Of An Aircraft To Follow A Flight Trajectory With At Least One Turn

ABSTRACT

Method and device for automatically monitoring the ability of an aircraft to follow a flight trajectory with at least one turn. 
     The monitoring device ( 1 ) includes means ( 6, 8, 10, 11, 14 ) for implementing monitorings in order to estimate the ability of the aircraft to follow at least one turn of the flight trajectory.

The present invention relates to a method and a device for automatically monitoring the ability of an aircraft, in particular of a transport airplane, to follow a flight trajectory comprising at least one turn.

Although not exclusively, the present invention more particularly applies to operations with required navigation performance with authorization required, of the RNP AR (<<Required Navigation Performance with Authorization Required>>) type. These RNP AR operations are based on a surface navigation of the RNAV (<<aRea NAVigation>>) type and on required navigation performance operations of the RNP (<<Required Navigation Performance>>) type. They have the particular feature of requiring a special authorization for being able to be implemented on an aircraft.

The RNAV type surface navigation allows an aircraft to fly from a waypoint to another waypoint, and no longer from ground stations (of radio-navigation means of the NAVAID type) to ground stations.

As known, the RNP concept corresponds to a surface navigation, for which (on board the aircraft) monitoring and warning means are added, allowing to ensure that the aircraft remains in a corridor, referred to as RNP, around a reference trajectory and authorizing taking into consideration curved trajectories. Outside this corridor, potentially relief or other aircrafts could be present. The performance required for a RNP type operation is defined by a RNP value representing half the width (in nautical miles: NM) of the corridor around the reference trajectory, in which the aircraft should remain 95% of the time during the operation. A second corridor (around the reference trajectory) of half a width twice the RNP value is also defined. The probability that the aircraft goes out of this second corridor should be lower than 10⁻⁷ per hour of flight.

The concept of RNP AR operations is still even more stringent. The RNP AR procedures are indeed characterized by:

-   -   RNP values:         -   being lower than or equal to 0.3 NM in approach, and that             could go down to 0.1 NM; and         -   being strictly lower than 1 NM at the start and during a             throttling up, and that could also go down to 0.1 NM;     -   a final approach segment that could be curved; and     -   obstacles (mountains, traffic, . . . ) that could be located at         twice the RNP value with respect to the reference trajectory,         while for usual RNP operations, an additional margin with         respect to obstacles is provided.

The air authorities have defined a target level of safety TLS (<<Target Level of Safety>>) of 10⁻⁷ per operation, whatever the type. In the case of RNP AR operations, as the RNP values can go down to 0.1 NM and the obstacles could be located at twice the RNP value of the reference trajectory, this objective results in a probability that the aircraft goes out of the half-width corridor D=2.RNP that should not exceed 10⁻⁷ per procedure.

The equipment on board aircrafts (flight management system, inertial unit, means for updating GPS data and means for guiding the autopilot), as well as the usual architecture, do not allow to reach the target level of safety, if mitigation operational means are not provided, including for detecting and managing possible breakdowns. This is why a special authorization is required for this type of operation, so as to ensure that the operational procedures and the pilots' training allow the target level of safety to be reached. Moreover, as the crew should take in charge some breakdowns, the aircrafts are to-day not able to guarantee a RNP value of 0.1 NM in a breakdown situation, as the crew are not able to meet the performance requirements in manual piloting.

On current aircrafts, the monitoring of RNP AR operations is implemented by means of two usual functions, that is:

-   -   a first function monitoring the accuracy and the integrity of         the position calculation:         -   the accuracy of the position is compared to once the RNP             value;         -   the integrity is compared to twice the RNP value; and         -   if one of the two parameters, accuracy or integrity, exceeds             the allotted threshold, a warning is emitted and the crew             should take appropriate actions; and     -   a second function allowing the crew to monitor the guidance of         the aircraft:         -   the lateral and vertical deviations of the aircraft with             respect to the reference trajectory are displayed and shown             to the crew;         -   the crew monitor the deviations compared to the budgets             allotted for each deviation. If the crew detects an             excessive deviation, they should keep the aircraft under             control again and take the adequate corrective actions.

As set forth previously, the current aircrafts are not able to guarantee a RNP value of 0.1 NM in a breakdown situation and the crew should be trained specially for flying the RNP AR procedures. The crew should, indeed, be able to detect and process, adequately, breakdowns being able to compromise the ongoing operation.

The objective for future aircrafts is to be able to fly RNP AR procedures with RNP values up to 0.1 NM, and this without restriction (in a normal situation and in the case of a breakdown) in start, approach and throttling up phases. To this end, the crew should no longer be considered as the main means for detecting and processing breakdowns.

The ability of an aircraft to follow a RNP AR trajectory comprising at least one turn, could be comprised under certain particular conditions, including in case of unfavourable winds. Under this type of conditions and depending on the wind force being encountered, the aircraft is sometimes no longer able to follow the defined trajectory. This type of problem could also occur when the speed of the aircraft exceeds a reference speed for the turn being started. This situation could, more specifically, occur as a result of a breakdown or of an error from the crew concerning a manually selected speed.

It is thus advantageous to be able to monitor the ability of the aircraft to meet the RNP AR performance. If the required performance level is not reached, the crew should be made aware of this, so as to be able to most appropriately react.

The present invention aims at solving the above mentioned drawbacks. It relates to a method for automatically monitoring the ability of an aircraft to follow a flight trajectory comprising at least one turn.

To this end, according to this invention, said method is remarkable in that, during a flight of the aircraft, for at least one turn of said flight trajectory, automatically:

a) the radius of said turn is determined;

b) a limit speed is determined up to which the aircraft may flight according to said turn without any risk of excursion of the flight trajectory;

c) a current speed value of the aircraft is determined;

d) said current speed value is compared to said limit speed; and

e) from this comparison, it is inferred:

-   -   if the current speed value is lower than or equal to said limit         speed, that the aircraft can fly according to said turn without         any risk of excursion; and     -   if the current speed value is higher than said limit speed, that         there is a risk of excursion.

Preferably, said steps c), d) and e) are repeatedly implemented, upon a flight of the aircraft.

Thereby, thanks to the invention, through comparing the current speed of the aircraft, in particular a current ground speed, to an appropriately calculated limit speed, it is possible to monitor the adaptation of the speed of the aircraft to the turn(s) to be encountered, that is the ability of the aircraft to follow its trajectory with no risk of excursion.

Monitoring according to this invention performance of follow up of a trajectory with turn(s) is particularly adapted to the RNP context, but could be extended to any guidance context implemented according to a flight plane.

Advantageously, at step e), a warning is emitted if there is a risk of excursion. Thus, if the required performance level is not met, the crew are made aware and are able to react in a most adapted way, either reducing its speed, or throttling up.

Additionally, advantageously, at step a):

-   -   the radius of the turn being considered is determined from data         (said radius of the turn or other data) extracted from an         on-board database; or     -   said radius of the turn is calculated from a nominal roll of         said turn.

Furthermore, in a preferred embodiment, the following operations are implemented:

-   -   at step b), a theoretical maximum speed is determined, up to         which the aircraft can fly according to said turn;     -   at step d), the current speed value is compared to said         theoretical maximum speed; and     -   at step e) from this comparison, it is inferred:         -   if the current speed value is lower than or equal to said             theoretical maximum speed, that the aircraft is not in             overspeed; and         -   if the current speed value is higher than said theoretical             maximum speed, that the aircraft is in overspeed.

In this case, preferably, at step e):

-   -   a warning is emitted in case of a risk of excursion without         overspeed; and     -   an alarm is emitted (being different from the warning) in the         case of overspeed.

Thus, the warning level (warning, alarm) can be adapted to the actual situation: a simple risk of excursion without overspeed or an overspeed.

Additionally, advantageously, at step b):

-   -   said theoretical maximum speed is calculated by means of a         maximum roll and of a turn radius extracted from a database; and     -   said limit speed can be calculated, either by means of a limit         roll and of a turn radius extracted from a database, either         subtracting a constant value at a theoretical maximum speed.

Furthermore, said steps a) to e) are implemented:

-   -   either for the whole of the turns in the flight trajectory of         the aircraft;     -   or for only a part of said turns, only analyzing the next turn         or a reduced number of next turns for example, that could be         enough for giving the crew some time to react in case of a         problem.

Furthermore, advantageously, at step e), an automatic regulation of the speed can also be implemented in the case of a risk of excursion.

The present invention further relates to a device for automatically monitoring the ability of an aircraft, in particular of a transport airplane, to follow a flight trajectory comprising at least one turn.

According to this invention, said device is remarkable in that it comprises:

-   -   means for determining, upon a flight of the aircraft, the radius         of at least one turn of said flight trajectory;     -   means for determining a limit speed, up to which the aircraft         can fly according to said turn without any risk of excursion of         the trajectory;     -   means for determining a current speed value of the aircraft;     -   means for comparing this current speed value to said limit         speed; and     -   means for inferring from this comparison:         -   if the current speed value is lower than or equal to said             limit speed, that the aircraft can fly according to said             turn without any risk of excursion of the flight trajectory;             and         -   if the current speed value is higher than said limit speed,             that there is a risk of excursion.

Moreover, in a preferred embodiment, said device further comprises:

-   -   means for determining a theoretical maximum speed, up to which         the aircraft can fly according to said turn;     -   means for comparing the current speed value to said theoretical         maximum speed; and     -   means for inferring from this comparison:         -   if the current speed value is lower than or equal to said             theoretical maximum speed, that the aircraft is not in             overspeed; and         -   if the current speed value is higher than said theoretical             maximum speed, that the aircraft is in overspeed.

The present invention further relates to:

-   -   a guidance system of the aircraft, comprising a monitoring         device, such as mentioned herein above; and/or     -   an aircraft, in particular a transport airplane, being provided         with such a guidance system and/or such a monitoring device.

The FIGS. of the appended drawing will better explain how this invention can be implemented. In these FIGS., like reference numerals relate to like components.

FIG. 1 is a block diagram of a device according to the invention.

FIGS. 2 to 4 are diagrams for explaining the main characteristics of this invention.

The device 1 according to this invention and schematically shown on FIG. 1 is provided for automatically monitoring the ability of an aircraft AC, in particular of a transport airplane, to follow a flight trajectory TV comprising turns VA, VB, VC, VD, while checking whether the aircraft AC is able to fly according to these turns VA, VB, VC, VD. This monitoring device 1 could be part of a guidance system 2 of the aircraft AC.

It is known that the navigation, in or out of a RNP context, is based on the information supplied by the flight plane. The latter is broken down in a succession of segments S1 to S6 defined in the side plane, as shown on FIG. 2. These segments could be of different types: segments of a straight line, such as S1, S3, S4, and S6, and circle arcs, such as S2 and S5. The turns VA, VB, VC being considered in the present invention could be basic segments of turn, such as S2 and S5, or a succession of two segments of a straight line, such as S3 and S4. For each turn VA, VB, VC of the flight plane, a navigation database 3 supplies its radius RA, RB, RC and the reference speed at which it should be started. The nominal roll angle applicable for following the described trajectory could be inferred from the previous parameters. Usually, a flight management system determines, from the position of the aircraft AC and from its attitude, parameters illustrating the deviation of the aircraft AC with respect to the trajectory TV. It also determines a nominal roll angle to be applied on the next segments, as a function of their radius of turn. From information being present in the flight plane and from data reflecting the position of the aircraft AC with respect to the flight trajectory TV, a usual transfer function with a large lateral loop calculates a turn initiation order of the aircraft AC. This order is afterwards transmitted to the small loop transfer function so as to slave the aircraft AC. Thereby, the flight management system calculates a turn initiation order being transferred to a flight control system for slaving the aircraft AC. This order could vary in a range comprised between +Φmax and −Φmax, for example between +30 and −30 degrees, with respect to an attitude of the aircraft AC with the wings being flat (illustrated in dashes on FIG. 3, upon a nominal operation. The extreme attitudes are represented on the two parts 4 and 5, on the left and on the right hand side, of FIG. 3. This range of values could, more specifically, be the authority limit of the large loop guidance.

As set forth above, the ability of an aircraft AC to follow a flight trajectory TV1 comprising at least one turn VD could be compromised under certain particular conditions including in the case of unfavourable winds, as shown on FIG. 4 where the wind is highlighted by means of arrows F. Under this type of conditions and depending on the force of the wind being encountered, the aircraft AC could no longer be able to follow the defined trajectory TV1 so as to fly according to a trajectory T1 going out of a corridor C defined around the trajectory TV1, for example a usual RNP corridor. This type of problem could also occur when the speed of the aircraft AC exceeds a reference speed for the turn VD being started. Such a situation could, more specifically, occur as a result of a breakdown or as a result of an error from the crew concerning the manually selected speed.

The device 1 according to this invention aims at monitoring the ability of the aircraft AC to follow its flight trajectory so as to be able to detect a situation such as mentioned hereinabove.

To this end, said device 1 on-board the aircraft AC, comprises according to the invention:

-   -   means 6 for determining, usually, for each turn being considered         VA, VB, VC, the radius RA, RB, RC of said turn. These means 6         are connected, preferably, via a link 7 to the database 3 and         either extract directly the radius from this database 3, or         calculate usually the radius from data extracted from this         database 3;     -   means 8 being connected via a link 9 to said means 6 and being         formed so as to determine a limit speed Vlim, up to which the         aircraft AC could fly according to said turn, without risk of         excursion of the trajectory TV;     -   means 10 for determining a current speed value Vc of the         aircraft AC;     -   means 11 being connected via links 12 and 13, respectively, to         said means 8 and 10 and being formed so as to compare this         current speed value Vc to said limit speed Vlim; and     -   means 14 being connected via a link 15 to said means 11 and         being formed so as to infer from the previous comparison:         -   as long as the current speed value Vc remains lower than or             equal to said limit speed Vlim, that the aircraft AC can fly             according to the turn being considered without any risk of             excursion; and         -   as soon as the current speed value Vc becomes higher than             said limit speed Vlim, that there is a risk of excursion.

Thus, through comparing the current speed Vc of the aircraft AC, in particular a current ground speed, to an appropriately calculated limit speed Vlim, said device 1 according to this invention is able to monitor the adaptation of the speed of the aircraft to the turn(s) to be encountered, that is the ability of the aircraft AC to follow its trajectory TV, and more specifically, to reach RNP AR performance.

Monitoring according to this invention is particularly adapted to the RNP context, but could be extended to any guidance context implemented according to a flight plane.

Said device 1 further comprises means 16 being connected via a link 17 to said means 14 and being formed so as to emit a warning, of the visual or sound type, in the cockpit of the aircraft AC, as soon as the means 14 consider that there is a risk of excursion. Thus, if the performance level is not met, the crew are immediately made aware and are able to react in a most adapted way, either manually reducing the speed of the aircraft AC, or controlling a throttling up.

This invention thus provides warnings to the crew, so that they are able to react accordingly should a problem occur, manually adjusting the speed of the aircraft AC. It is also possible to implement an automatic regulation of the speed of the aircraft AC.

To this end, in a particular embodiment, said device 1 further comprises means 18 being connected via a link 19 to said means 14 and being formed so as to implement an automatic regulation of the speed in the case of a risk of excursion, preferably bounding it systematically to the limit speed Vlim. If, however, the automatic regulation of the speed does not allow meeting the desired performance level, this approach could be completed by relevantly selected warning levels (and emitted by the means 16).

Moreover, in a preferred embodiment, said device 1 further comprises:

-   -   means 20 being connected via a link 21 to said means 6 and being         formed so as to determine a theoretical maximum speed Vmax, up         to which the aircraft AC can fly according to the turn being         considered;     -   means 22 being connected via links 23 and respectively to said         means 20 and 10 and being formed so as to compare the current         speed value Vc (received from the means 10) to said theoretical         maximum speed Vmax; and     -   said means 14 being connected via a link 25 to said means 22 and         being formed so as to infer from the previous comparison:         -   as long as the current speed value Vc remains lower than or             equal to said theoretical maximum speed Vmax, that the             aircraft AC is not in overspeed; and         -   as soon as the current speed value Vc becomes higher than             said theoretical maximum speed Vmax, that the aircraft AC is             in overspeed.

In such a case, the means 16 are formed so as:

-   -   to emit a warning, of the visual or sound type, in the cockpit         of the aircraft A, as soon as the means 14 consider that there         is a risk of excursion; and     -   to emit in the cockpit of the aircraft A an alarm, also of the         visual or sound type, but being different from said warning, and         this as soon as the means 14 consider that there is a case of         overspeed.

Thus, the warning level can be adapted (warning, alarm) to the actual situation: a simple risk of excursion without overspeed or an overspeed.

Furthermore, the means 10 determine usually the current speed Vc of the aircraft AC in a referential adapted for the implementation context. This could be the speed of the aircraft AC relative to the speed of the air or even the speed of the aircraft AC in the ground benchmark, for instance. In order that any turn could be triggered without risk of excursion, it is thus advisable to compare the current speed Vc to the limit speed Vlim for ensuring that the speed of the aircraft AC is adapted for the trajectory to be followed, for instance, for ensuring that the speed of the aircraft AC allows to remain on a trajectory of the RNP type, despite unfavourable winds. The theoretical maximum speed Vmax may be employed as a complement for evaluating the level of risk, to which the current speed Vc submits the aircraft AC.

Furthermore, the means 8 calculate said limit speed Vlim based on the following expression:

Vlim=√{square root over (R.g.tg(Φlim))}

wherein:

-   -   R represents the radius of the turn being considered;     -   tg represents the tangent;     -   g represents the gravity acceleration; and     -   ølim corresponds to a limit, preferably predetermined, roll, for         instance 20°.

Furthermore, the means 20 calculate said theoretical maximum speed Vmax based on the following expression:

Vmax=√{square root over (R.g.tg(Φmax))}

wherein ømax corresponds to a maximum, preferably predetermined, roll, for instance 30° as shown on FIG. 3.

Being integrated into the systems involved in the guidance loop of the guidance system 2 (being only partially shown on FIG. 1), the device 1 could be implemented according to different embodiments. In a first embodiment, the whole of the means of said device 1, except means 10 and 18, are integrated into a flight management system of the FMS (<<Flight Management System>>) type. In this first embodiment, monitoring is therefore concentrated in the flight management system then operating directly on the data extracted from its navigation database 3.

Furthermore, in a second embodiment, including the means 8, 11, 14, 16, 20, and 22 of said device 1 are integrated into a Flight Control and Guidance System of the FCGS type. In this second embodiment, monitoring is distributed between the FCGS and FMS systems, the FMS system supplying in particular the information relative to the flight plane.

It should be noticed, in an alternative, that, contrarily to the previously detailed principle, for which a controlled roll margin ølim is determined on a constant basis, a speed margin could also be selected as constant CS. In this case, the device 1 can calculate the limit speed Vlim from the following relationship:

Vlim=Vmax−CS

With a constant speed margin CS and depending on the selected value, it is possible to tolerate higher rolls for high ground speeds.

The previously presented approaches are based on data or radiuses of turn extracted from the navigation database 3. It is also possible to rely on a turn nominal roll, allowing the means 6 to infer the radius of the turn. To this end, it is known that on the current flight management systems FMS, the nominal roll of the turn is calculated for each turn of the flight plane.

A particular application of the device 1 according to this invention relates to a monitoring covering all the future turns on an ongoing RNP procedure. However, it could also be contemplated that the device 1 only monitors a sub-part of all these turns, only analyzing the or one reduced number of next turns, that could be sufficient for giving the crew some time to react should a problem occur. Beyond a certain number of next turns, the current speed of the aircraft AC in the ground benchmark is no longer able to be implemented: a prediction of the ground speed of the aircraft AC could then be used for implementing this invention. 

1. A method for automatically monitoring the ability of an aircraft (AC) to follow a flight trajectory (TV) comprising at least one turn (VA, VB, VC, VD), a method wherein during a flight of the aircraft (AC), for at least one turn of said flight trajectory (TV), automatically: a) the radius (RA, RB, RC) of said turn (VA, VB, VC) is determined; b) a limit speed is determined from the thus determined radius; c) a current speed value of the aircraft (AC) is determined; d) said current speed value is compared to said limit speed; and e) from this comparison, it is inferred: if the current speed value is lower than or equal to said limit speed, that the aircraft (AC) can fly according to said turn without any risk of excursion of the flight trajectory (TV); and if the current speed value is higher than said limit speed, that there is a risk of excursion of the flight trajectory (TV).
 2. The method according to claim 1, wherein at step a), said radius of the turn is determined from data extracted from an on-board database (3).
 3. The method according to claim 1, wherein at step a), said radius of the turn is calculated from a nominal roll of said turn.
 4. The method according to claim 1, wherein said steps c), d) and e) are repeatedly implemented, upon a flight of the aircraft (AC).
 5. The method according to claim 1, wherein, in addition: at step b), a theoretical maximum speed is determined, up to which the aircraft (AC) can fly according to said turn; at step d), the current speed value is compared to said theoretical maximum speed; and at step e) from this comparison, it is inferred: if the current speed value is lower than or equal to said theoretical maximum speed, that the aircraft (AC) is not in overspeed; and if the current speed value is higher than said theoretical maximum speed, that the aircraft (AC) is in overspeed.
 6. The method according to claim 5, wherein at step b), said theoretical maximum speed Vmax is calculated from the following expression: Vmax=√{square root over (R.g.tg(φmax))} wherein: R represents said radius of the turn; tg represents a tangent; g represents the gravity acceleration; and ømax corresponds to a maximum roll.
 7. The method according to claim 1, wherein at step b), said limit speed is calculated from the following expression: Vlim=√{square root over (R.g.tg(Φlim) )} wherein: R represents said radius of the turn; tg represents a tangent; g represents the gravity acceleration; and ølim corresponds to a limit roll.
 8. The method according to claim 1, wherein at step b), for calculating said limit speed Vlim, a constant value is subtracted at a theoretical maximum speed determined from the radius of the turn.
 9. A method according to claim 1, wherein said steps a) to e) are implemented for at least one part of the turns of said flight trajectory (TV).
 10. The method according to claim 1, wherein at step e), a warning is emitted if there is a risk of excursion.
 11. The method according to claim 5, wherein at step e): a warning is emitted in case of a risk of excursion without overspeed; and an alarm is emitted in case of an overspeed.
 12. The method according to claim 1, wherein at step e), an automatic regulation of the speed is implemented in the case of a risk of excursion.
 13. A device for automatically monitoring the ability of an aircraft (AC) to follow a flight trajectory (TV) comprising at least one turn (VA, VB, VC, VD), said device (1) comprising: means (6) for determining, upon a flight of the aircraft (AC), the radius of at least one turn (VA, VB, VC, VD) of said flight trajectory (TV); means (8) for determining a limit speed from the thus determined radius; means (10) for determining a current speed value of said aircraft (AC); means (11) for comparing this current speed value to said limit speed; and means (14) for inferring from this comparison: if the current speed value is lower than or equal to said limit speed, that the aircraft (AC) can fly according to said turn without any risk of excursion of the flight trajectory (TV); and if the current speed value is higher than said limit speed, that there is a risk of excursion of the flight trajectory (TV).
 14. The device according to claim 13, wherein it further comprises: means (20) for determining a theoretical maximum speed, up to which the aircraft (AC) can fly according to said turn; means (21) for comparing the current speed value to said theoretical maximum speed; and means (14) for inferring from this comparison: if the current speed value is lower or equal to said theoretical maximum speed, that the aircraft (AC) is not in overspeed; and if the current speed value is higher than said theoretical maximum speed, that the aircraft (AC) is in overspeed.
 15. An aircraft, wherein comprising a device (1) such as specified in claim
 13. 